Pentaborate(1-) salts and a tetraborate(2-) salt derived from C₂- or C₃-linked bis(alkylammonium) dications: Synthesis, characterization, and structural (XRD) Studies

The synthesis of a number of pentaborate(1-) salts from cations arising from N-substituted α,α-, α,β-, and α,γ-diaminoalkanes has been attempted in aqueous solution from B(OH) 3 and the appropriate diammine in a 10:1 ratio. Despite relatively mild work-up conditions the pentaborate(1-) salts prepared were not always as anticipated and the following compounds were isolated in good yield: [Me 2NH(CH 2) 2NHMe 2][B 5O 6(OH) 4] 2 ( 1), [Et 2NH(CH 2) 2NHEt 2][B 5O 6(OH) 4] 2 ( 2), [Et 2NH 2][B 5O 6(OH) 4] ( 3), [Me 2NH 2][B 5O 6(OH) 4] ( 4), [Me 2NH(CH 2) 3NHMe 2][B 5O 6(OH) 4] 2 ( 5), [Et 2NH(CH 2) 3NHEt 2][B 5O 6(OH) 4] 2 ( 6), [Me 3NCH 2CH=CH 2][B 5O 6(OH) 4] ( 7), and [Me 3N(CH 2) 3NMe 3] [B 5O 6(OH) 4] 2 .0.5H 2O ( 8). The tetraborate(2-) salt, [Me 3N(CH 2) 2NMe 3][B 4O 5(OH) 4] .2B(OH) 3 .2H 2O ( 9) was obtained in moderate yield (41%) from a 3:1 reaction of B(OH) 3 with [Me 3N(CH 2) 2NMe 3](OH) 2. All compounds were characterized by spectroscopy ( 1H, 11B, 13C NMR and IR) and thermal gravimetric analysis (TGA). BET analysis on materials derived thermally from selected samples ( 1, 2, 6, 7) all had porosities of < 1 m 2/g, demonstrating that they were non-porous. Single-crystal XRD structures were obtained for 2, 3, 7, 8 and 9 and all contain extensive H-bonded polyborate lattices.